The present invention constitutes an improvement over my copending patent application Ser. No. 416,996 filed Sept. 13, 1982, to which reference is made for further background. It is often desirable to have made available a hydraulically actuated downhole pump assembly which can be designed in a manner whereby the power piston and production plunger reciprocate an unusually long stroke. It is also desirable that such a pump assembly require a minimum of moving parts, thereby greatly extending the life of the pump because there are fewer parts subject to malfunction. It is further desirable to have a long stroking pump assembly which utilizes the power fluid for lifting the power piston uphole as the production plunger makes the suction stroke, and thereafter, utilizes the stored energy of the produced fluid for returning the power piston in a downhole direction while concurrently forcing the production plunger to make a power stroke.
The present invention provides a new downhole hydraulically actuated pump of either the free or fixed type which achieves the above desirable goals, and at the same time overcomes many of the disadvantages found in similar downhole pumps. A downhole pump made in accordance with the present invention has an unexpected long life because of the novel features associated therewith.